1. Field of the Invention
The present invention relates to an optical pick-up actuator, and more particularly, to an optical pick-up actuator capable of recording data on an optical recording medium or reproducing data recorded on an optical recording medium.
2. Description of the Related Art
An optical pick-up actuator moves a lens holder with an objective lens, and maintains the position of the objective lens at a fixed position with respect to an optical recording medium. The optical pick-up actuator follows the track of an optical recording medium to record data and reproduce data recorded on the optical recording medium.
FIG. 1 is a perspective view of an optical pick-up actuator according to the related art, and FIG. 2 is a magnetic circuit of an optical pick-up actuator according to the related art.
Referring to FIGS. 1 and 2, the optical pick-up actuator includes an objective lens 201 formed in a lens holder 202 in a central portion thereof, and a magnetic circuit formed at the side thereof for driving the lens holder 202. The magnetic circuit includes a focusing coil 205 and tracking coil 206, a tilt coil 217, a yoke 203, and multi-pole-magnetized magnets 204a, 204b, 204c, and 204d. 
As shown in FIGS. 1 and 2, on both the left and right sides of the lens holder 202 are focusing coils 205 (for performing focusing) attached in mutual opposition with respect to a vertical boundary between polarizations of the magnets (204a and 204c) and (204b and 204d), and in the central portions of the left and right sides of the lens holder 202 are tracking coils 206 (for performing tracking) attached in mutual opposition with respect to a horizontal boundary between polarizations of the magnets 204a and 204b. 
Also, a tilt coil 217 is formed on the peripheral surface of the lens holder 202 opposite to the horizontal boundary 204 of the magnets. The tilt coil 217 functions as a radial tilt coil.
A magnet 204 may be a single magnet with multiple poles or may consist of four unidirectional magnets.
Magnets 204 having multiple poles are respectively fastened on an inner surface of a yoke 203 of a ferromagnetic material to the left and right of the lens holder 202, and the yoke 203 is integrally formed through a joining means with a pick-up base (not shown).
One end of a wire suspension 207 is fixed to upper and lower portions on the central side surface of the lens holder 202, and the other end of the wire suspension 207 is fixed to a main substrate through a frame 209 provided at one end of the lens holder 202. The wire suspension 207 levitates the lens holder 202, and also functions as an intermediary wire that supplies a current.
Here, a damper (not shown) is formed inside the frame 209 for endowing the rigid wire suspension 207 with damping characteristics, and the other end of the wire suspension 207 is fixed to the main substrate (not shown) that is attached outside through soldering.
Referring to FIG. 3, an explanation of the operation of an optical pick-up actuator will be given.
When current flows in the focusing coil 205, the focusing coil 205 and the magnet 204 having multiple poles mutually act to exert a force in a vertical direction on the focusing coil 205. Accordingly, the lens holder 202 moves in a focusing direction (vertically).
When current flows in the tracking coil 206, the tracking coil 206 and the magnet 204 having multiple poles mutually act to exert a force in a horizontal direction on the tracking coil 206. Accordingly, the lens holder 202 moves in a tracking direction (horizontally).
As shown in FIG. 2, when current flows in the tilt coil 217 wound around the perimeter of the lens holder 202, the tilt coil 217 and the multi-pole magnets 204a and 204b mutually act to exert forces in opposite directions with respect to the left and right sides of the tilt coil 217.
If the lens holder 202 moving in conjunction with the mounted coils 205 and 206 is called a moving coil method, a converse movement of the lens holder 202 with a magnet mounted thereto is called a moving magnet method.
Such an optical pick-up actuator operates as a moving coil by means of a magnetic field of permanent magnets, to move the objective lens to a predetermined desired location on an optical recording medium. That is, the lens holder 202 is fixed by the wire suspension 207, and must be moved in focusing and tracking directions without errors occurring.
However, as shown in FIG. 3, when moving in a tracking direction of the lens holder, the weight center (WC) and the force center (TC) do not match, so that the device operates in a rolling mode in high-threshold frequencies.
That is, the weight center in a vertical direction is the center of the lens holder 202, whereas the force (F) in a tracking direction has a center located at the center of the tracking coil 206, so that there is a distance d between the weight center and the force center. When the lens holder 202 moves in a tracking direction, there is the problem of torque (Fd) created at the force center of the tracking coil 206.